Electrolytic device



May 3, 1938.

P. ROBINSON ELECTROLYTIC DEVICE Filed June 9, 1956' R. m ON E mam Wm w Patented May 3, 1938 UNITED STATES PATENT OFFICE EECTRDLYTIC DEVICE Application Jane 9, 1938, Serial No. 84,341

lzclaims.

'filming metal, in a hydrated or unhydrated form. Of the above filming metals aluminum is most...

widely used and I shall therefore describe my invention in connection with aluminum electrodes. The electrodes are usually wound into a roll or assembled into a stack with the interposition of a film-maintaining viscous electrolyte. The viscosity of the electrolyte may vary within a wide range from that of a slightly viscous liquid that of an almost solid mass. I

The electrolyte is usually-although not necessarilycarried by a spacer, which also acts as a separator, and may consist of one or more layers of gauze, paper, cellophane and the like. According to the circuits in which the dry electrolytic condensers are used, they iall into two groups. of these the so-called D. C. condensers are used in circuits in which a rectified and pre-' dominantly unidirectional current prevails, for example in filter or by-pass circuits of radio apparatus. These condensers have usually only one 30 filmed electrode, which is the anode.

On the other hand, the so-called A. C. candensers are used in circuits where an A. C. current fiows or predominates, for example. as starting condensers of capacitor motors. In these 35 condensers as a rule both electrodes are filmed. My invention applies primarily to A. C. dry electrolytic condensers, although it is also .of considerable usefulness for D. C. dry condensers which operate at a much lower voltage than at which their film has been formed.

The A. C. condensers and also D. C.- condensers -so far the latter are used at a much lower operating voltage than at which their film has been formed-show a very marked deterioration as. in operation. This deterioration, the exact reason of which has not been determined, seems to come about becauseof a gradual reductionof the thickness of the eflective film during opera.- tion, although the actual physical thickness of so the film remains substantially unchanged. The

reduction of the effective thickness of the illm. manifests itself by an increase of the capacity of the condenser, which increase of capacity isalso accompanied by an increase Both the increase of capacity and .of

of the power factor...

power factor cause the heat developed in the condenser to increase, which in turn further increases the capacity of the film and the power factor. Thusthe effect is cumulative and causes deterioration of the condenser with increasing 5 rapidity.

While it is possible to considerably reduce such deterioration of A. C. condensers' by negatively biasing the electrolyte, such measure is impractical in mostuses of these condensers, as it re- 10 quires the provision of a separate source of D. C. bias, which is eitherunfeasible or even if feasible too costly.

I have-found that the above deterioration of the film can be prevented or at least greatly re- 15 duced by using in the formation of the electrode film certain selected electrolytes, or by using certain selected electrolytes as final electrolyte in the condensers and preferably by combining these two measures.-

, While a large number of various electrolytes has been suggested for film-formation and also as final or filling electrolyte for dry electrolytic condensers, both the forming and final-electrolytes now used are generally of the borate types, i. e., the ionogen is boric acid and/or a salt of boric acid; this because it has been found that such borate electrolytes result in films having for a given thickness'higher resistance, higher breakdown voltage, and lower power factor than the films obtained with other electrolytes, and give the condensers better all-round characteristics in operation.

I have found that while the borate electrolytes have indeed the various advantages above enu- -merated, they are by their nature responsible for bringing about the above referred to deterioration of the film in A. C. use (and in referring to A. C. use I also include'here the D. C. use of condensers of which the "operating voltage is much-below the forming voltage of their film), or at least are unsuccessful in preventing same.

On the other hand I have found that other electrolytes, and particularly electrolytes comprising phosphoric acid and/or salts thereof--and hereafter referred to as phosphate electrolyteswhile.,,being in a general way less suited for v electrolytic condensers than are borate electrolytes, have inherently the property of preventing the above referred to deterioration of the film or of counteracting the same.

It seems that this advantage of phosphate electrolytes-andthis advantage is also shared to someextent by some other electrolytes particularly those containing oxalates and chromatestill I am well aware that phosphate electrolytes have been suggested in the past for electrolytic condensers; however, having been found much inferior to borate electrolytes for reasons above stated, and particularly on account or the greater acidity of the phosphoric acid compared with boric acid, and also because of the diidculties involved in. a suitable pasty electrolyte for dry condensers w ches phates, phosphate electrolytes have not in practice.

According to my invention l the gen erel advantages oi borate electrolytes with the particular advantage or phosphate electro ytes ct preventing deterioration of the illin hi ll. C.

The condensers made in accordance with my invention have the further advantage oi exceed ingly good shelf lite and are also to op erate at much higher temperatures than are the condensers previously available.

This I obtain by using one or both steps of my invention, these steps being briefly the roller? ing: (a) the use or a phosphate forming ele trolyte; (b) the use of a'small addition of phow phate in the final electrolyte. To obtahn the best results and full advantage of my invention, It pre for to combine both steps, although each oi the above steps produces individually considerable improvement.

It should be understood that suitable substitutes for phosphates are other acid radicals such chromates and oiralates, which ioiin aluminum compounds which are insoluble in the tinsel elec= trolyte.

As a forming electrolyte I prefer to use aqueous solution of a phosphate with a pill usual ly greater than 6 and preferably above 7, tor en ample, an aqueous solution of 5% disodium phosphate without any ,further addition, which is somewhat alkaline.

Electrodes formed in such an electrolyte under the conditions later to be stated, will have a film which shows a great resistance to deterioration A. 0. use of the condenser, even if used in a born-to electrolyte without further addition.

Instead of using as final electrolyte a bore-rte electrolyte without any addition, I prefer to cold to it about 3% to 2% and preferably 32% to 5% of a phosphate. For example, I may use an elec trolyte comprising 5%-3b% water (this per centage representing the liquid portion of the electrolyte), 5% disodlum phosphate, and the remainder glycol and ammonium penteborate in the proportion of 2 parts of glycol and 3 parts or ammonium pentaborate.

In general, the final electrolytes suitable for such condensers should have a pl-l value of about t to 5, and the addition of the phosphate or other suitable salt (as oxalate or chromete) should he sufiiciently small to permit the pH value to re= main within the above limits.

As a, rule I prefer the addition oi very small amounts of such salts, as the beneficial efiect obtained by such additions manifests itself usually to substantially the full extent even when the additions amount only to 2% to 5% of the electrolyte. Although greater amounts of these salts as a rule have no deleterious influence as long as the pH remains within the specified range, I have found that in many instances the addition ofgreater amounts is objectionable because of the difidculty of properly dissolving them in the electrolyte. For example, in case of disodlum phosphate with the ionizingsolvents and bcrates usually employed, amounts higher than 2% in volve difliculties in dissolving the disodiuni phosphate.

This and similar final electrolytes give very good results even if the film has been formed in a borate electrolyte; however the results are tar superior with a film formed in a phosphate elcc trolyte oi the above type.

My invention will be described in connection with some specific examples and the accompahy lug drawing, in which:

Figure l is a perspective view of an A. (3'. dry electrolytic condenser embodying the invention.

The condenser shown in Fig. l is, for example, a starting condenser for a capacitor motor, and consists of two electrode foils i-i oi aluminum foil provided with a film made in accordance with the invention.

Prior to him formation the electrodes may be etched by known methods.

The formation of the film on the aluminum toil talres place in an aqueous solution which is preferably a phosphate solution and preferably also a solution which has a pH higher than 6 and usual ly higher than 7, thus being on the alkaline side. A very suitable solution is, for example, an aqueous solution of .5% disodium phosphate.

However, when forming the aluminum foil in a solution or such a high pll value, even if the solution is slightly on the acidic side, secondary re actions take place which consist mainly in the chemical attack of the aluminum by the phosphate solution.

This chemical attack is the stronger, the higher the pH value of the solution. On the other hand, in the-case of phosphate electrolytes the film resistance and brealrdovm voltage increases with increased pl-l values of the forming electrolyte, and thus to obtain a high resistant and high breakdown voltage film, in a single formation, the use of a high pH value phosphate electrolyte is required.

l have succeeded in forming in high pH value phosphate electrolytes with a negligible attack of the: aluminum by such electrolytes, by using a very high speed of formation. This high speed formation it obtain by forming the aluminum foil in. a continuous process in accordance with-the processes of my copending patent applications Ser. no. 5%,270, filed July 1, 1931, now Patent No. anemia and Ser. l lo. 741,493, filed August 225, i934, now Patent No. 2,057,315 whereby it immediately apply the full forming voltage to the aluminum foil and pass the foil through the ziorrning electrolyte at a rate of about 30 it. per minute. As some of the electrolyte m carried. over mechanically by the foil, I prefer to immediately subject the foil after its passage through the forming electrolyte .to washing in distilled water and-to subsequent drying. Thereby any reaction of the electrolyte with the aluminum is prevented after the film formation.

For a lid-volt condenser a forming voltage of about. loll volts is used, and preferably the full voltage is immediately applied to the foil.

If the condenseris designed for higher voltages, I prefer to subject the filmed electrode to a second formation in a'borate electrolyte, for example in case of a 220-volt starting condenser, I subject the electrode to a formation at 320 volts in a solution of borax and boric acid. 'In this case, the conditions of the initial phosphate formation may vary over wider limits than those given above.

The electrodes so formed and provided with terminals 5 are wound into a roll usually, although not necessarily, with the interposition of spacers 3-4 which may consist of one or more layers of paper, gauze, cellophane and the like. Although the electrolyte may be applied to the spacer before the assembly of the condenser roll, I prefer to impregnate the wound condensers, for example by means of centrifugal impregnation.

The electrolyte used may be a viscous paste comprising as a solvent 9. polyhydric alcohol and water, and as ionogen a borate and a small amount of phosphate. A suitable electrolyte is one comprising 5% to 30% of water (the water being expressed in percentage of the liquid portion of the electrolyte), .5% disodium phosphate, the remainder being ethylene glycol and ammonium pentaborate in the proportion of two parts of glycol and three parts of ammonium pentaborate. Instead of using .5% disodium phosphate, a smaller or larger percentage of such salt can be used. the range of 0.2-2% having been found suitable; the same range of addition has also been found generally suitable for other phosphates as well as other salts which can be used instead of phosphates, such as oxalates or chromates. In general the exact amount of additions depends on various factors, of which the desired pH value of the electrolyte (which should be usually between 4 and 5) and the resistance of the electrolyte which is preferably somewhat higher than 100 ohms. per centimeter cube. (measured at 100 C.) are the most important. ,The above given limits are therefore to be regardd only asindicative of the order of the amounts of such additions, and not as exact limiting values.

The condensers so obtained will have a very muchlower initial power factor than prior art condensers and will maintain their initial prop erties during their contemplated life.

A series of tests made with three groups of condensers, the condensers of which were identical in every respect except that the forming and final electrolytes for the diflerent groups were different, will illustrate the radical improvement obtained with my invention.

a The first group of condensers had films formed in a borate electrolyte and had a borate final electrolyte.

The second group had films formed in a phosphate forming electrolyte, in accordance with the invention, but used a borate final electrolyte.

The third group had films formed in a phosphate forming electrolyte and a phosphate-containing final electrolyte, both in accordance with the invention.

For the same forming voltage and the same electrolyte resistance, the first group showed an average initial power factor of about 4.5%; the second group an average initial power factor of about 3.5%, and the itial power factor of about 3%..

The condensers were subjected to one of the 5 usual tests prescribed for starting condensers,

third group an average innamely to a continuous life test up to a point where the power factor hasincreased by 50%.

The first group of condensers after three hours, continuous use had a power factor of about 6.75%, which corresponds to the values usually found with the previously available dry electrolytic starting condensers. The second .group of condensers had an averagepower factor of about 5.25% after 30 hours, whereas the third group of condensers had an average power factor of about 3.75% after 100 hours use.

Thus it will be noted that the improvement obtained in accordance with my invention is quite startling; and as a 100 hours continuous testis a more severe test than 500,000 intermittent uses corresponding to 500,000 startings of the motor, a condition to which no condenser would be subjected in actual use; it can be said that condensers made in accordance with the invention will not be subjected in their use to any marked film deterioration.

Besides the above advantages condensers made in accordance with the invention are characterized-by exceedingly high stability both with regard to shelf life, as well as with regard to their maintaining their desired characteristics at very high operating temperature.

For example, while prior to the present invention, dry electrolytic starting condensers could not be used at operating temperatures above 55 C., the condensers made in accordance with the invention, operate entirely satisfactoril. up to 80 C. and even higher.

This, besides other advantages, makes it possible to place these condensers inside of the housing of the capacitor motor, a construction which has been long aimed at and yet only achieved with the prior art condensers, if auxiliary cooling means were used.

The invention is particularly important in connection with condensers using etched foil electrodes. In such condensers, because of their smaller size for a given capacity compared with condensers using unetched foils, a larger amount of heat is developed in operation per unit of volume of condenser. Because of the stable characteristic of the condenser made in accordance with the invention at higher temperatures, it is possible to use the small sized etched foil-condensers in many applications where formerly because of the excessive heat developed in same they could not be used.

A similar improvement of the condensers is valso obtained in other A. C. uses, as well as D. C.

uses when the forming voltage greatly exceeds the operating voltage.

While I have described my invention in con-' nection with specific examples and in specific applications, I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

In the claims the terms "borate and phosphate are to include the salts of boricand phosphoric acid respectively, the acids themselves, as well as combinations of the respective salts and acid.

What I claim is:

1. In the manufacture of dry electrolytic condensers, the process which comprises, electrolytically forming a film on a filming electrode in a phosphate electrolyte, and assembling said electrode, in a condenser having a viscous electrolyte comprising as ionogen a borate and a small addition of phosphate.

2. In the manufacture of dry electrolytic condensers, the process which comprises, electrolytically forming a film on a filming electrode in a phosphate electrolyte having a pH greater than 6, and using said filmed electrode in a condenser having a viscous electrolyte comprising as ionogen a borate and a small addition of phosphate.

3. In the manufacture of dry electrolytic condensers, the process which comprises, electrolytically forming a film on an aluminum electrode in a weak aqueous solution of disodium phosphate and using said electrode in a condenser having a viscous borate-containing electrolyte.

4. In the manufacture of dry electrolytic condensers, the process which comprises, electrolytically forming a film on an aluminum electrode in an alkaline electrolyte comprising as major constituent an aqueous solution of a phosphate, and at a speed of formation suificiently high to minimize chemical attack of the electrolyte on the aluminum.

5. In the manufacture of A. C. dry condensers for intermittent use, the process which comprises, subjecting filming electrodes to a forma-' tion in an aqueous solution of a phosphate electrolyte at a voltage of the order of 160 volts, subsequently subjecting prior to use said electrode to a second formation in a borate electrolyte at a voltage which is in excess of said first forming voltage and of the operating voltage of the condensers and operating said electrodes in condensers having a viscous borate electrolyte comprising a small addition of a phosphate.

6. A dry electrolytic condenser having two electrodes, at least one of which is of filming metal and provided with a film, and a viscous electrolyte interposed between said electrodes, said electrolyte comprising as ionogens a borate and an addition of phosphate, the latter constitilting about 0.2% to 2% of the electrolyte.

7. In a dry electrolytic condenser, two electrodes, at least one of which is of filming metal and provided with a film, a viscous electrolyte interposed between said electrode, said electrolyte comprising as ionogen a borate and a compound of the group consisting of phosphates,

chromates and oxalates, which compound forms electrodes, and a viscous electrolyte interposed between same, said viscous electrolyte comprising as ionogens a borate and an addition of phosphate, the latter constituting about 0.2% to 2% of the electrolyte.

10. A dry electrolytic condenser comprising two electrodes, of which at least one is of filming metal and provided with a film, and a viscous electrolyte interposed between same, said electrolyte comprising .2%-1% disodium phosphate, 5% to 30% of water, the remainder being ethylene glycol and ammonium pentaborate.

11. A dry electrolytic condenser comprising two electrodes of which at least one is of film-forming metal and provided with a film, and a viscous electrolyte interposed between said electrodes, said electrolyte comprising as ionogen a borate and a compound oi the group consisting of phosphates, chromates and oxalates added thereto in an amount of about 0.2% to 2% of the electrolyte, said condenser having stable characteristics at an operating temperature up to 80 C.

12. In the manufacture of dry electrolytic condensers, the process which comprises, electrolytically forming a film on an aluminum electrode in an electrolyte comprising as major constituent an aqueous solution of a phosphate, and operating said electrode in a condenser having an electrolyte comprising as ionogen a borate and a small addition of a salt of the group consisting of phosphates, chromates and oxalates, which salt forms an insoluble compound with aluminum oxide.

PRESTON ROBINSON. 

